Method of making welded bi-metal piston rings



B. M. RONAY Sept. 19, 1961 METHOD OF MAKING WELDED BI-METAL PISTON RINGS 2 Sheets $heet 1 Filed March 20, 1956 FIG.2.

FIGI

INVENTOR 152 DR M. RONAY ATTORNEYS B. M. RONAY 3,000,080

METHOD OF MAKING WELDED BIMETAL PISTON muss Sept. 19, 1961 2 Sheets-Sheet 2 Filed March 20, 1956 Micro-Structure of Cast Iron Piston Ring Flg. 413

Fig. -1-1;

ETCHED CONDITION UNETCHED CONDITION m cro-Structure of Bi-Mctal Piston Ring wsw UNETCHED CONDITION Fig. 5B

ETCHED CONDITION INVENTOR B E LA M; RONAY BY I AETORNEY U i ed S at s he 3,000,080 METHOD OF MAKING WELDED. BI-METAL PISTON RINGS Bela M. Ronay, 24 Randall St., Annapolis, Md. Filed Mar. 20, 1956, Ser. No. 585,600

4 Claims. (Cl. 29156.6) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to piston rings and particularly to improvements in metallic piston rings, such as are adapted for use in internal coinbustion'engines, and to a "novel process of manufacturing-such piston rings;

The function of piston rings in internal combustion engines isto seal the annular clearance space between the cylinder wall or liner and the piston. The heat of combustion of fuel introduced in the space above the piston quickly heats the small volume of the piston rings and they expand against the wall of the cylinder liner. This The standard material from which piston rings are made is cast iron, because it ofiers the best wear resistance against the vcylinder liners. However, the low fatigue and high creep values ofcast ironare responsible for the limited life of piston rings,.for example, in high compression, high temperature diesel engines. Design of 1 diesel cnginescompensates somewhat for this shortcoming of such piston rings by arrangements which permit quick disassembling of the engine head so that the piston rings can be replaced within short outage periods. In

free piston engines, replacement of piston rings requires complete disassembling of. the engine, causing extended outage periods. Because pressures and temperatures in free piston engines are higher than in crankshaft type diesels, the life of the presently available all cast iron piston rings is even shorter than in conventional diesel engines, requiring more frequent replacements. This causes unduly high percentage of outage periods.

It is therefore a principal object of this invention to provide a piston ring which overcomes the above mentioned defects of prior piston rings.

A further object of this invention is to provide long life piston rings.

A more specific object of this invention is to provide a piston ring incorporating desirable features of an all cast iron piston ring while eliminating undesirable characteristics thereof.

Another specific object of this invention is to provide a piston ring incorporating desirable features of a steel piston ring while eliminating undesirable characteristics thereof.

Another object of this invention is to provide a novel process of manufacturing my improved piston rings and this process forms the subject matter of the claims of the instant application. The piston ring is the subject matter of a divisional application.

The above and other objects and advantages of the invention will be more apparent from a perusal of the following specification and accompanying drawings.

Specifically, the above objects of the invention are accomplished by the use of a novel layered bi-metal combination comprising a core of low alloy steel and a welded-on overlay of cast iron. The core of alloy steel is relatively tough and resilient, and the overlay of cast iron is relatively soft and brittle.

In the drawings:

FIG. 1 is a side elevation, partly in section, of a builtup, bi-metal cylinder, in accordance with this invention, from which the piston rings are cut;

FIG. 2 is a transverse section taken on line 2-2 of FIG. 1;

' FIG. 3 is a vertical section on an enlarged scale, through a finished bi-metal piston ring in accordance with this invention, taken substantially on line 3--3 of FIG. 2;

FIG. 4A is a photomicrograph of a cross-section of a conventional cast iron piston ring in unetched condition; FIG. 4B is a photomicrograph of the same specimen, as in FIG. 4A, in etched condition;

FIG. 5A is a photomicrograph of a cross-section of a bi-metal pistonring in accordance with this invention, in unetched condition; and

FIG. 5B is a photomicrograph of the same specimen, as in FIG. 5A, in etched condition.

The above photomicrographs are all taken at the same magnification, that is, diameters.

Referring now to FIG. 1 of the drawings, 10 designates a built-up, bi-metal cylinder comprising a core 11 and a welded-on overlay 12. The core of the cylinder comprises an alloy steel whose endurance value at the applied temperature. range permits unlimited stress revers als' developing in the hinge-like alternations of the finished piston ring, and whose low creep at the service temperature permits the development and maintenance of the required stress to produce the hinge-like movement during the life of the ring. It has been found in practice that low alloy steels of 1 /2 to 2V2% chromium and A: to 1%molybdenum content are excellent metals for thecore 11. 'For exceptional cases, the core material "may be chromium nickel type austenitic steel. 40

The overlay 12 comprises a welded-on layer, or layers as desired, of cast iron. The composition and microstructure of the cast iron overlay, as to quality and size of free graphite particles, is comparable with those pre vailing inconventional, all cast iron piston rings. Such micro-structure is developed by a combination of selection of the composition of the cast iron and the welding technique used, as described hereinafter.

In practising the process of the instant invention, to assure that the bond between the outer layer of cast iron and the alloy steel core of the ring remains intact during the life of the ring, the cast iron is applied as a welded-on overlay. The weld rod, which preferably consists of total carbon, 3.90%, silicon, 3.10% max., maganese, 0.80% max., phosphorus, 0.80% max., sulphur, 0.12% max., and the balance substantially iron, is fused onto the core by an acetylene flame or other applicable welding process; the welds comprising continuous overlapping beads built up into layers. To obtain in the cast iron overlay the desired microstructure as to size, quantity and dispersion of the free graphite particles and having an overwhelmingly pearlite matrix, the cooling rate is regulated in the course of welding.

This regulation consists of preheating the core to be overlaid to 700 to 900 F. range and maintaining this temperature during deposition of the cast iron overlay. Further, to prevent development of preferential cooling of the overlay and thus assure uniformity of dispersion of the free graphite flakes therein, the thickness of each layer deposited is restricted. In this respect, the heat block of the preheated mass of the core tube is of further assistance. The abundance of the pearlite constituents thus produced in the slowly cooled assembly rings.

Thus, it is seen, by this invention, there provided a novel piston ring and anovel process or producing long life, bi-metal piston rings by applying cast iron to a low alloy steel core by welding, wherein the low alloy steel chosen is the type which retains a high percentage of its room temperature yield and fatigue strength at service temperatures, wherein the application Di cast iron by welding in the manner of this invention esfl res 100% bonding between the core material and the overlay, and

wherein the isothermal post heat treatment develops particles in the welded.on cast iron overlay were iound to give the new piston ring 25% more .wear lite th the conventional all cast iron ring.

It should be understood, of course, thatflie t regoins relates to only a preferred embodiment of the invention aud'that numerous modifications or alterations'may be made therein without departing from the spirit and the scope of the invention as set forth in the rappsndede lainls.

What is claimed is: 1. The method of forming layered piston .rings'having an outer overlay that is relatively soft and brittle and :an inner core that is relatively tough and resili nt WhiQh comprises the steps of preheating a preformed cylinder of low chrome molybdenum alloy steel to a temperature of approximately 700 to 900 F., while holding the 7 cylinder at such temperature welding and overlay of piston ring cast iron onto the outer surface thereof by oxy-acetylene welding, and cooling the resultant product to develop a substantially 100% pearlitic structure therein.

2. The method of forming piston rings as set forth 4 in claim 1 wherein the overlay of cast iron is applied to the preheated cylinder in a manner as to cause uniformity of dispersion of free graphite flakes and development of substantially pearlite in the cast iron overlay.

3. The method of forming piston rings as set forth in claim 1 wherein the. preformed cylinder consists essentially of low chrome-molybdenum steel comprising 1.5 t 25% hromiu an 9-5 to 1 0% moly den 4. The method of forming G-type bi-metal piston rings ha in a steel inner su face a d ss s iron outer s a which comprises preheating a preformed low chrome molybdenum all y st el cylinder to a tempera ur f 700 to w lding built-inn layer 9 p st n rin ast iron onthe outer surface at the st el Cylinder by (my-acetylene welding while maintain ng the p hea temperatur the eof, machin ng the ou er surfac of the cast ir n bui t-up t a cylindrical s rtace concent is h t e nner surface of the ste l sylinder, cut ng sepa ate s from said b .lt-np cylinder, and sli ting the separate in s- Refer n s Cited. in h 1 at this paten UNITED STATES PATENTS 1,327,098 Kellogg et a1. Ian. 6, 1920 1,618,665 Lloyd flu Feb. 22, 1927 1,856,279 May 3, 1932 1,951,397 Mar. 20, 1934 2,189,595 Feb. 6, 1940 2,214,651 Sept. '10, 1940 2,281,426 Farr Apr. 28, 1942 7 2,311,240 Marien Feb. 16, 1943 2,565,042. Phillips g Aug. 21, 1951 2,696,038 Hunt Beat], 1954 FOREIGN PATENTS 471,517 Great'Britain May 1 5, 1936 471,565 Great Britain a May 15, 1936 698,345 Germany Nov. 7, 1940 Q HER REFERENCES Factors A-flfecting Cylinder and Ring Wear of Diesel Engines, by Dr. Tracy C. Jarrett, pp; 38=40, Diesel Power and Diesel Transportation, May. 1950.

Digest of Steels for High Temperature Service, fifth edition, 194.6, publishedby The Timken Roller Bearing Company, Steel and Tube Division, Canton .6, Qhio. (Copy available in Div. 3.) 

1. THE METHOD OF FORMING LAYERED PISTON RINGS HAVING AN OUTER OVERLAY THAT IS RELATIVELY SOFT AND BRITTLE AND AN INNER CORE THAT IS RELATIVELY TOUGH AND RESILIENT WHICH COMPRISES THE STEPS OF PREHEATING A PREFORMED CYLINDER OF LOW CHROME MOLYBDENUM ALLOY STEEL TO A TEMPERATURE OF APPROXIMATELY 700* TO 900*F., WHILE HOLDING THE CYLINDER AT SUCH TEMPERATURE WELDING AND OVERLAY OF PISTON RING CAST IRON ONTO THE OUTER SURFACE THEREOF BY OXY-ACETYLENE WELDING AND COOLING THE RESULTING PRODUCT TO DEVELOP A SUBSTANTIALLY 100% PEARLITIC STRUCTURE THEREIN. 